Does a civil engineer whose work unintentionally caused a fatal accident bear the burden of diyah (blood money) or kaffarah (expiation), even though he did not order the placement of the stone that caused the accident?

Repentance is obligatory for failing to secure the safety device. The responsible authorities should hold the negligent accountable. As for blood money (diyya), expiation (kaffarah), and car insurance, these are not binding on the questioner, because he did not directly cause the accident or contribute to it by placing the stone, as there is no liability without direct causation or contribution.